Preparing cigarette filters

ABSTRACT

Cigarette filters are made by passing a continuous rod of filter material continuously through a moving die to form a continuous filter element having a repeated pattern of staggered grooves so arranged that the continuous filter element can be cut at regular intervals to form individual filter elements each having in its peripheral surface a number of grooves extending substantially axially alternately from opposite ends of the element.

This invention is concerned with a cigarette filter comprising a filterelement closely surrounded by a wrapper, the filter element being formedin its peripheral surface with grooves extending substantially axiallyinto the element alternately from opposite ends of the element so as todefine a number of circumferentially spaced passages through whichcigarette smoke can enter the filter, and a number of circumferentiallyspaced axial passages through which the smoke can leave the filter afterpassing through the ribs formed between the grooves. In other words,each groove extends from one end of the filter element and stops shortof the other end. The smoke is filtered during its passage through theribs.

The total flow area for the smoke through the ribs can be made largecompared with the cross-sectional area of a conventional filter of thesame diameter, so that the smoke velocity through the filtering materialis relatively low and the filtering efficiency is relatively high for agiven pressure drop through the filter.

There may for example be three or four grooves extending axially intothe filter element from each end, making a total of six or eightgrooves.

A filter according to this invention is preferably made by forming acontinuous filter element which is then cut at regular intervals(preferably after being enclosed in a continuous wrapper) to formindividual sections for cigarettes. The continuous cigarette filterelement is preferably formed by passing filter element material througha die comprising a number of die parts each having a die surface whichis movable towards and away from the centre of the die and is so shapedthat the continuous filter element formed by the passage of the materialthrough the die has a repeated patern of staggered grooves so arrangedthat the continuous filter element can be cut at regular intervals toform individual filter elements each having in its peripheral surface anumber of grooves extending substantially axially alternately from theopposite ends of the element. The arrangement of the grooves is suchthat when the continuous element is cut into short sections atappropriate positions, each section when surrounded by a wrapper makesup a filter in the form already described.

The die through which the filter material is extruded preferablycomprises a number of co-operating wheels driven at the same speed asthe filter element material, each wheel being formed with at least onecircumferentially extending rib which forms one of the grooves in thecontinuous filter element during each revolution of the wheel. Thefilter material may be supplied to the die as an already formed rod, therod being simply shaped in the appropriate manner by the die.

The filter element may for example be formed from cellulose acetate towwith sufficient plasticizer to enable the cellulose acetate to hold itsshape after being formed with the grooves.

An example of a filter element and of a method of manufacture accordingto the present invention will now be desribed with reference to theaccompanying drawings. In these drawings:

FIG. 1 shows a continuous filter which is to be cut into individualfilter sections;

FIG. 2 is a cross-section through the filter element, showing the diewheels which shape the continuous filter element;

FIG. 3 is a perspective view of the filter element for a singlecigarette;

FIG. 4 is a side view of part of a cigarette, with the wrapping brokenaway to show the filter element; and

FIG. 5 is a section on the line V--V in FIG. 4.

As shown in FIG. 1, the continuous filter consists of a filter element 2surrounded by a wrapper 4. This continous filter is cut at regularlyspaced lines 6 (which represent the pattern-repeat points of the groovesin the filter element) to form double-length filters. Each double-lengthfilter is then joined between two cigarette lengths by means of a stripof joining paper which is wrapped and glued round the filter with itssides overlapping onto the cigarette lengths. Each double-lengthfilter-tipped cigarette is then cut across the middle (i.e. in effect atlines 8 in FIG. 1) to separate the double cigarette into individualfilter-tipped cigarettes.

As shown particularly by FIG. 3, each filter element consists of fourcircumferentially spaced V-sectioned grooves 10 which extend into thefilter from one end and stop short of the other end, while between thesegrooves 10 there are four similar grooves 12 which extend into thefilter from the opposite end and again stop short of passing rightthrough the filter element. Accordingly in the completed cigarette asshown in FIG. 4, smoke from a cigarette length 13 passes into the filterthrough the grooves 12 and leaves the filter to enter the smoker's mouththrough the grooves 10, having passed transversely through the ribs 14formed between the grooves. It should be noted, as shown in FIG. 5, thatthe grooves are so shaped in cross-section that the ribs 14 haveparallel sides; thus the resistance to smoke flow through the ribs isuniform.

As shown in FIG. 4, the filter is joined to the cigarette length by astrip of paper or other material 15 which is glued round the filter andoverlaps onto the cigarette length.

As shown in FIG. 2, the continuous filter element is extruded to therequired shape by a die consisting of four similar wheels 16, of whichonly one is shown complete with its drive shaft 18. The axes of rotationof the four wheels are all in a common plane. The filter elementmaterial, for example a tow of cellulose acetate or other fibrousmaterial, is passed through the die in a direction normal to this commonplane. Thus the fibres of the tow extend longitudially in the finishedfilter element. The peripheral surfaces of the wheels together form amoving die surface. Each wheel in the particular example shown has fourV-sectioned ribs 20; that is two on each side of a central plane throughthe wheel. The ribs on opposite sides of the central plane are staggeredin the appropriate manner to form the staggered grooves in thecontinuous filter element.

The filter element material may, for example, be fed to the die in theform of a rod of approximately the same diameter as the finished filterelement.

It will be appreciated that the wheels are all driven at a speed such asto produce a peripheral velocity equal to the velocity of the filterelement material passing through the die formed by the wheels. In otherwords the wheels act by rolling the filter element material into therequired shape.

Instead of the continuous filter element being enclosed in a wrappingbefore it is cut into double-filter lengths, it may be cut intodouble-filter lengths before being enclosed in a wrapping. In this casethe wrapping for the filter may be the paper which joins the filter tothe cigarette length. In other words, in FIG. 4 the filter element maybe surrounded only by the layer 15 of paper or other wrapping materialwhich in this case would be glued round the filter element and to theend of the cigarette length.

We claim:
 1. A method for making cigarette filters comprising(a) formingfilter material into a continuous rod, (b) feeding said continuous rodof filter material along a predetermined path, (c) shaping thecontinuous rod by at least one moving die which provides said rod with aplurality of circumferentially-spaced longitudinally-extending rows ofgrooves separated by a plurality of longitudinally extending ribsadapted for flow of cigarette smoke therethrough in a directiontransverse to the axis of the rod, each row comprising a plurality ofindividual elongated grooves arranged successively in spaced end-to-endrelationship in a longitudinal direction with filter material occupyingthe space between the ends of adjacent grooves in each row and eachgroove of each row overlapping longitudinally with at least twosuccessive grooves of each adjacent row of grooves, each rib extendingcontinuously between adjacent rows of grooves, and (d) cutting theformed continuous rod at the space between the ends of successivegrooves in at least one row into filter lengths such that none of thegrooves in said filter lengths fully extend between opposite endsthereof.
 2. A method according to claim 1 comprising forming a pluralityof circumferentially spaced V-sectioned grooves with a longitudinallyextending rib between each groove of each row at least two successivegrooves of each adjacent row of grooves, said V-sectioned grooves beingso shaped in cross-section that substantially parallel sides are formedon said ribs to maintain uniform flow of smoke through said ribs betweenadjacent grooves in different rows.
 3. A method according to claim 1comprising forming grooves of substantially the same length, the groovesof alternate rows being axially aligned, and cutting the filter materialat the space between the ends of successive grooves of said alternaterows.
 4. A method according to claim 3 comprising cutting the filtermaterial at the space between the ends of successive grooves of the rowsintermediate said alternate rows.
 5. A method according to claim 1comprising(a) rotating a plurality of wheels, each having at least onerib projecting from the peripheral surface thereof, arranged with theirperipheries forming a moving die about said path, and (b) feeding saidcontinuous rod through said moving die to form said grooves in saidcontinuous rod.
 6. A method according to claim 1 .[.in which thecontinuous rod is enclosed.]. .Iadd.comprising enclosing the continuousrod .Iaddend.in a continuous wrapper and .[.is.]. then .[.cut.]..Iadd.cutting the wrapped continous rod .Iaddend.into .[.the.]. doublefilter lengths for joining between two cigarette lengths.
 7. A methodfor making cigarette filters comprising(a) forming filter material intoa continuous rod, (b) feeding said continuous rod of flter materialalong a predetermined path, (c) rotating a plurality of wheels arrangedwith their peripheries forming a moving die about said path, each ofsaid wheels having at least one rib projecting from the peripheralsurface thereof on each side of a central plane through the wheel, theribs on one side of the central plane being staggered with respect tothe ribs on the opposite side of the central plane to form saidcontinuous rod with a plurality of circumferentially-spacedlongitudinally-extending rows of grooves, each row comprising aplurality of grooves arranged successively in a longitudinal directionand each groove of each row overlapping longitudinally with at least twosuccessive grooves of each adjacent row of grooves, and (d) cutting theformed continuous rod between the successive grooves in at least one rowinto lengths. .Iadd.
 8. In a method for making ciagarette filters(a)forming filter material into a continuous rod, (b) feeding saidcontinuous rod of filter material along a predetermined path, (c)shaping the continuous rod by at least one moving die which providessaid rod with a plurality of rows of grooves separated by a plurality ofcontinuous elongated ribs adapted for flow of cigarette smoketherethrough in a direction tranverse to the axis of the rod, each rowcomprising a plurality of individual elongated grooves arrangedsuccessively in spaced end-to-end relationship with filter materialoccupying the space between the ends of adjacent grooves in each row,and each groove of each row overlapping with at least a portion of eachof at least two successive grooves of each adjacent row of grooves, and(d) cutting the formed continuous rod into individual filter lengthssuch that none of said grooves in said filter lengths fully extendbetween opposite ends thereof..Iaddend. .Iadd.9. In a method for makingcigarette filters (a) forming filter material into a continuous rod, (b)feeding said continuous rod of filter material along a predeterminedpath, (c) shaping the continuous rod by at least one moving die whichprovides said rod with a plurality of rows of grooves separated by aplurality of continuous elongated ribs adapted for flow of cigarettesmoke therethrough in a direction transverse to the axis of the rod,each row comprising a plurality of individual elongated grooves arrangedsuccessively in spaced end-to-end relationship with filter materialoccupying the space between the ends of adjacent grooves in each row,and each space between the ends of adjacent grooves in each row beinglocated between the ends of a groove in each adjacent row of grooves,and (d) cutting the formed continuous rod into individual filter lengthssuch that none of said grooves in said filter lengths fully extendbetween opposite ends thereof..Iaddend. .Iadd.10. In a method for makingcigarette filters (a) forming filter material into a continuous rod, (b)feeding said continuous rod of filter material along a predeterminedpath, (c) shaping the continuous rod by at least one moving die whichprovides said rod with a plurality of rows of grooves separated by aplurality of continuous elongated ribs adapted for flow of cigarettesmoke therethrough in a direction transverse to the axis of the rod,each row comprising a plurality of individual elongated grooves ofpredetermined length arranged successively in spaced end-to-endrelationship with filter material occupying the space between the endsof adjacent grooves in each row, and each space between the ends ofadjacent grooves in each row being located between the ends of a groovein each adjacent row of grooves, and (d) cutting the formed continuousrod into individual filter lengths such that none of said grooves insaid filter lengths fully extend between opposite ends thereof.